Method of routing electrical current to bodily tissues via implanted passive conductors

ABSTRACT

The invention provides an implant, system and method for electrically stimulating a target tissue to either activate or block neural impulses. The implant provides a conductive pathway for a portion of electrical current flowing between surface electrodes positioned on the skin and transmits that current to the target tissue. The implant has a passive electrical conductor of sufficient length to extend from subcutaneous tissue located below a surface cathodic electrode to the target tissue. The conductor has a pick-up end which forms an electrical termination having a sufficient surface area to allow a sufficient portion of the electrical current to flow through the conductor, in preference to flowing through body tissue between the surface electrodes, such that the target tissue is stimulated to either activate or block neural impulses. The conductor also has a stimulating end which forms an electrical termination for delivering the current to the target body tissue.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a Continuation of U.S. patent application Ser. No.13/850,760, entitled “Method of Routing Electrical Current To BodilyTissues Via Implanted Passive Conductors,” filed Mar. 26, 2013, which isa Continuation of U.S. patent application Ser. No. 12/400,202, filedMar. 9, 2009, now U.S. Pat. No. 8,406,886, which is a Continuation ofU.S. patent application Ser. No. 11/337,824, filed Jan. 23, 2006, nowU.S. Pat. No. 7,502,652, which is a Continuation-in-Part ofInternational Application No. PCT/CA2005/000074 filed Jan. 24, 2005,which claims priority from U.S. Provisional Application No. 60/538,618filed Jan. 22, 2004. Each of the aforementioned applications isincorporated herein in its entirety by reference.

BACKGROUND

The present invention relates to an implant, system and method fortreating a disorder of the nervous system in a subject. The methodinvolves using passive electrical conductors which route electricalcurrent to electrically stimulate a target body tissue to eitheractivate or block neural impulses depending upon the frequency and thedisorder to be treated.

Nerve cells consist of an axon for transmitting action potentials orneural impulses, and dendrites for receiving such impulses. Normally,nerves transmit action potentials from the impulse-sending axon of onenerve cell to the impulse-receiving dendrites of an adjacent nerve cell.At synapses, the axon secretes neurotransmitters to trigger thereceptors on the next nerve cell's dendrites to initiate a newelectrical current.

In some pathological states, transmission of action potentials isimpaired; thus, activation of neural impulses is required to restorenormal functioning. Electrically-excitable bodily tissues such as nervesand muscles may be activated by an electrical field applied betweenelectrodes applied externally to the skin. Electric current flowsthrough the skin between a cathode electrode and an anode electrode,eliciting action potentials in the nerves and muscles underlying theelectrodes. This method has been used for many years in different typesof stimulators, including transcutaneous electrical nerve stimulators(TENS) which relieve pain, therapeutic electrical stimulators whichactivate muscles for exercise purposes (Vodovnik, 1981), functionalelectrical stimulators which activate muscles for tasks of daily life(Kralj et al., 1989); U.S. Pat. No. 5,330,516 to Nathan; U.S. Pat. No.5,562,707 to Prochazka et al.) and stimulators that promote regenerationof damaged bones.

In other pathological states, action potentials are transmitted which donot serve a useful purpose; hence, blocking of unnecessary neuralimpulses is required to restore normal functioning. It has been reportedthat high-frequency stimulation can produce temporary reversible blocksof nerve axons (Solomonow et al., 1983; Tai et al., 2004; Bhadra andKilgore, 2005). Generally, the frequency range is between 500 and 30,000Hz.

Stimulation of nerves to either active or block neural impulses istypically achieved with the use of an implanted stimulator (also knownas a neural prosthesis or neuroprosthesis) (Peckham et al., 2001; Horchand Dhillon, 2004). Neural prostheses have been developed to restorehearing, to restore movement in paralyzed muscles, to modulate activityin nerves controlling urinary tract function and to suppress pain andtremor. In some cases, neural prostheses are designed to inhibit orsuppress unwanted neural activity, for example to block pain sensationor tremors. However, all neural prostheses intended for long-term userequire the implantation of a stimulator that contains electroniccomponents and often a battery. In the case of pain and tremorsuppression, the activated nerves reflexly inhibit the activity ofneural circuits within the central nervous system. This indirect mode ofreducing unwanted neural activity is sometimes called neuromodulation(Landau and Levy, 1993; Groen and Bosch, 2001).

Surface electrical stimulators are used reflexly for example to reducespastic hypertonus (Vodovnik et al., 1984; Apkarian and Naumann, 1991).A disadvantage of stimulation through electrodes attached to the bodysurface is that many non-targeted tissues may be co-activated along withthe targeted tissues. This lack of selectivity often causes unwantedsensations and/or unwanted movements. Furthermore, tissues that lie deepwithin the body are difficult or impossible to stimulate adequately,because most of the electrical current flowing between the electrodesflows through tissues closer to the electrodes than the targetedtissues. Selectivity may be improved by implanting wires within the bodythat route electrical current from a stimulator to the vicinity of thetargeted tissues. This method is used in cardiac pacemakers (Horch etal., 2004), dorsal column stimulators (Waltz, 1997), deep brainstimulators (Benabid et al., 1987) and sacral root stimulators (Brindleyet al., 1982). Cuffs containing the uninsulated ends of the wires may beplaced around peripheral nerves to restrict most of the current to thevicinity of the nerve and limiting the spread of current to surroundingtissues, thereby improving selectivity (Haugland et al., 1999).Generally when wires are implanted, the stimulators, complete with anenergy source, are also implanted (Strojnik et al., 1987). Implantedstimulators are expensive and often require a controller and/or powersource external to the body. Batteries within the implanted stimulatorsneed periodic replacement, entailing surgery.

In a minority of cases, stimulating wires are implanted in bodilytissues and led through the skin (percutaneously) to a connectorattached to the surface of the body, to which an external stimulator isattached (Peckham et al., 1980; Handa et al., 1998; Shaker and Hassouna,1999; Yu et al., 2001). External stimulators are much less expensivethan implanted stimulators, but the percutaneous wires provide a conduitfor infection and therefore require daily cleaning and maintenance. Thishas generally limited the use of percutaneous electrodes to short-termapplications. There is a need for a system which overcomes such problemsand has the capability of activating or blocking nerve impulsesdepending upon the disorder to be treated.

SUMMARY

The present invention broadly relates to an implant, system and methodusing passive electrical conductors which route electrical current toelectrically stimulate a target body tissue to either activate or blockneural impulses depending upon the frequency and the disorder to betreated.

In one aspect, the present invention broadly provides an implant forelectrically stimulating a target body tissue in a subject, the implant,once implanted, providing a conductive pathway for at least a portion ofthe electrical current flowing between surface cathodic and anodicelectrodes positioned in spaced relationship on the subject's skin andtransmitting that portion of the electrical current to the target bodytissue, the implant comprising:

a passive electrical conductor of sufficient length to extend, onceimplanted, from subcutaneous tissue located below the surface cathodicelectrode to the target body tissue, the electrical conductor having apick-up end and a stimulating end and being insulated between its ends,the pick-up end forming an electrical termination having a sufficientsurface area to allow a sufficient portion of the electrical current toflow through the conductor, in preference to flowing through body tissuebetween the surface cathodic and anodic electrodes, such that the targetbody tissue is stimulated, and the stimulating end forming an electricaltermination for delivering the portion of electrical current to thetarget body tissue.

In another aspect, the invention provides a system for electricallystimulating a target body tissue in a subject comprising the aboveimplant, together with

surface cathodic and anodic electrodes for making electrical contactwith the subject's skin, and which, when positioned in spacedrelationship on the subject's skin, for transmitting electrical currentto the target body tissue; and

a stimulator external to the subject's body, electrically connected tothe surface cathodic and anodic electrodes, the stimulator supplyingdirect, pulsatile, or alternating current to the surface cathodic andanodic electrodes.

In another aspect, the invention provides a method for electricallystimulating a target body tissue in a subject comprising the steps of:

providing the above implant;

implanting the implant entirely under the subject's skin, with thepick-up end positioned in subcutaneous tissue located below the surfacecathodic electrode, and the stimulating end positioned proximate to thetarget body tissue;

positioning the surface cathodic and anodic electrodes in spacedrelationship on the subject's skin, with the surface cathodic electrodepositioned over the pick-up end of the electrical conductor so theportion of the current is transmitted through the conductor to thetarget body tissue, and so that the current flows through the targetbody tissue and returns to the anodic surface electrode through bodytissues or through an implanted electrical return conductor extendingbetween the target body tissue and subcutaneous tissue located below thesurface anodic electrode; and

applying direct, pulsatile or alternating electrical current between thesurface cathodic electrode and the surface anodic electrode to cause theportion of the electrical current to flow through the implant sufficientto stimulate the target body tissue.

In yet another aspect, the present invention provides a method oftreating a disorder in a subject comprising the steps of:

providing an implant to act as a conductive pathway for at least aportion of the electrical current flowing between surface cathodic andanodic electrodes positioned in spaced relationship on the subject'sskin and transmitting the portion of the electrical current to thetarget body tissue, the implant comprising a passive electricalconductor of sufficient length to extend, once implanted, fromsubcutaneous tissue located below the surface cathodic electrode to thetarget body tissue, the electrical conductor having a pick-up end and astimulating end and being insulated between its ends, the pick-up endforming an electrical termination having a sufficient surface area toallow a sufficient portion of the electrical current to flow through theconductor, in preference to flowing through body tissue between thesurface cathodic and anodic electrodes, such that the target body tissueis blocked, and the stimulating end forming an electrical terminationfor delivering the portion of electrical current to the target bodytissue;

implanting the implant entirely under the subject's skin, with thepick-up end positioned in subcutaneous tissue located below the surfacecathodic electrode, and the stimulating end positioned proximate to thetarget body tissue;

positioning the surface cathodic and anodic electrodes in spacedrelationship on the subject's skin, with the surface cathodic electrodepositioned over the pick-up end of the electrical conductor so theportion of the current is transmitted through the conductor to thetarget body tissue, and so that the current flows through the targetbody tissue and returns to the anodic surface electrode through bodytissues or through an implanted electrical return conductor extendingbetween the target body tissue and subcutaneous tissue located below thesurface anodic electrode; and

applying electrical current between the surface cathodic electrode andthe surface anodic electrode in the form of a cyclical waveform at afrequency capable of blocking the target body tissue so as to treat thedisorder.

As used herein and in the claims, the terms and phrases set out belowhave the following definitions.

“Blocking” or “block” is meant to refer to preventing the conduction orpropagation of action potentials or nerve impulses along the axons of atarget nerve partially or completely.

“Body tissue” is meant to refer to a neural tissue (in the peripheral orcentral nervous system), a nerve, a muscle (skeletal, respiratory, orcardiac muscle) or an organ, for example, the brain, cochlea, opticnerve, heart, bladder, urethra, kidneys and bones.

“Cyclical waveform” means any form of electrical current in a repeatingwaveform without limitation to its shape or form, including withoutlimitation alternating current, pulsatile, sinusoidal, triangular,rectangular and sawtooth waveforms.

“Disorder” is meant to include movement disorders, muscular disorders,incontinence, urinary retention, pain, epilepsy, cerebrovasculardisorders, sleep disorders, autonomic disorders, disorders of vision,hearing and balance, and neuropsychiatric disorders.

“Electrical current” is meant to refer to current applied at the surfaceof the skin that is resistively and capacitively coupled to theimplanted passive conductor, which in turn conveys the current to thetarget neural tissue.

“Subject” means an animal including a human.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic three-dimensional view of an embodiment of theinvention having an implanted electrical conductor, surface cathodic andanodic electrodes, and an implanted electrical return conductor.

FIG. 2 is a side elevation view, in section, of an embodiment of theinvention having an implanted electrical conductor and surface cathodicand anodic electrodes.

FIG. 3 is a side elevation view, in section, of an alternate embodimentof the invention having an implanted electrical conductor, surfacecathodic and anodic electrodes, and an electrical return conductor.

FIG. 4 is a side elevation view, in section, of an alternate embodimentof the invention having two implanted electrical conductors, two surfacecathodic electrodes, an anodic electrode, and an electrical returnconductor.

FIGS. 5A and 5B are graphs showing the effect of frequency and amplitudeon pudendal nerve blocking. FIG. 5A shows the maximum decrease inurethral pressure elicited by stimulation of the pudendal nerve atdifferent amplitudes and frequencies, with the maximum decrease definedas the difference between the intraurethral pressure just prior to andduring high frequency stimulation. FIG. 5B shows the difference betweenbackground intraurethral pressure and the intraurethral pressureobtained during high frequency stimulation at different amplitudes andfrequencies.

FIGS. 6A and 6B are graphs showing the effect of stimulation amplitudesof 1 mA (FIG. 6A) and 3 mA (FIG. 6B) with a frequency of 1 kHz onpudendal nerve blocking in one animal.

FIGS. 7A and 7B are graphs showing the effect of stimulation amplitudesof 6 mA (FIG. 7A) and 3 mA (FIG. 7B) with a frequency of 2 kHz onpudendal nerve blocking in one animal.

FIG. 8 is a graph showing the relationship between urethral pressure andbladder pressure during pudendal nerve blocking in one animal.

DETAILED DESCRIPTION

The invention broadly provides an implant for electrically stimulating atarget body tissue in a subject to either activate or block neuralimpulses depending upon the frequency and the disorder to be treated.Once implanted, the implant provides a conductive pathway for at least aportion of the electrical current flowing between surface cathodic andanodic electrodes positioned in spaced relationship on a subject's skin,and transmits that portion of electrical current to the target bodytissue to either activate or block neural impulses. In further aspects,the invention provides a system and method incorporating the implant.

The subject can be an animal including a human. The body tissue can be aneural tissue (in the peripheral or central nervous system), a nerve, amuscle (skeletal, respiratory, or cardiac muscle) or an organ, forexample, the brain, cochlea, optic nerve, heart, bladder, urethra,kidneys and bones.

The invention can be applied to treat various conditions in whichstimulation to either activate or block neural impulses is required.Such conditions can include movement disorders (e.g., spasticity,hypertonus, rigidity, tremor and/or muscle weakness, Parkinson'sdisease, dystonia, cerebral palsy), muscular disorders (e.g., musculardystrophy), incontinence (e.g., urinary bladder disorders), urinaryretention, pain (e.g., migraine headaches, neck and back pain, painresulting from other medical conditions), epilepsy (e.g., generalizedand partial seizure disorder), cerebrovascular disorders (e.g., strokes,aneurysms), sleep disorders (e.g., sleep apnea), autonomic disorders(e.g., gastrointestinal disorders, cardiovascular disorders), disordersof vision, hearing and balance, and neuropsychiatric disorders (e.g.,depression). The invention may also be used for promoting bone growth(as required, for example, in the healing of a fracture), wound healingor tissue regeneration.

For stimulation of a target body tissue, particular frequencies to beapplied depend upon many factors; for example, the type of nerve to beblocked, the tissue which the nerve innervates, the size of the nerve,the subject to be treated, the type of condition, the severity of thecondition, and the receptiveness of the subject to the treatment. Ingeneral, for blocking, high frequencies are useful, for example, thecyclical waveform can be applied at a frequency in the range of between100 and 30,000 Hz, or alternatively in the range of between 100 and20,000 Hz. Still alternatively, the cyclical waveform can be applied ata frequency in the range of between 100 and 10,000 Hz, or in the rangebetween 200 and 5,000 Hz. For activation, low frequencies are generallyused, for example, a frequency in the range of between 1 and 100 Hz, oralternatively, in the range of between 1 and 50 Hz. Still alternatively,the frequency can be in the range of between 1 and 20 Hz.

A. The Router System

The invention is described with reference to the drawings in which likeparts are labeled with the same numbers in FIGS. 1 to 4. The inventionis shown generally in FIG. 1 which schematically illustrates portions ofa subject's body tissues, including skin 10, a nerve 12 with itsoverlying nerve sheath 14, and a muscle 16. FIG. 1 also illustrates animplant indicated generally at 18, a surface cathodic electrode 20 and asurface anodic electrode 22. The implant 18 is provided for electricallystimulating a target body tissue, such as a nerve 12, in a subject toeither activate or block neural impulses. Once implanted, the implant 18provides a conductive pathway for at least a portion of the electricalcurrent flowing between the surface cathodic and anodic electrodes 20,22.

When positioned in spaced relationship on the subject's skin 10, thesurface cathodic and anodic electrodes 20, 22 make electrical contactwith the skin 10 and transmit electrical current to the target bodytissue. Surface cathodic and anodic electrodes 20, 22 can be selectedfrom a conductive plate or sheet, a conductive gel electrode, aconductive rubber or polymer electrode that may be partially coated withan electrode paste or gel, or a moistened absorbent pad electrode.Self-adhesive hydrogel electrodes of the type used to stimulate muscles,with surface areas of 1 square centimeter or more are particularlyeffective. Platinum iridium electrodes, which are composed typically of80% or more platinum and 20% or less iridium, can also be used (forexample, 85% platinum-15% iridium alloy; 90% platinum-10% iridiumalloy). The positions of the surface cathodic and anodic electrodes 20,22 on the skin 10 may vary, depending upon the location and nature ofthe target body tissue.

A plurality of surface electrodes 20, 22 may be fabricated on a singlenon-conductive substrate to form an electrode array that may beconveniently attached to the skin 10 in one maneuver. Similarly, theplurality of terminations 30 of implanted conductors 24 may befabricated on a substrate to form an array. By matching the physicallayout of the surface electrode array to that of the implantedterminations array, a good spatial correspondence of surface andimplanted conductors may be achieved in a convenient and reproduciblemanner. Surface electrode arrays in which the conductivity of eachelement of the array may be independently controlled could also be usedto adjust the conductivity between the surface electrodes and theterminations in an implanted array.

The implant 18 comprises a passive electrical conductor 24 of sufficientlength to extend, once implanted, from subcutaneous tissue located belowthe surface cathodic electrode 20 to the target body tissue, for examplenerve 12. The electrical conductor 24 can be formed from a metal wire,carbon fibers, a conductive rubber or other conductive polymer, or aconductive salt solution in rubber. Multistranded, TEFLON®-insulated,stainless-steel wire conductors of the type used in cardiac pacemakerleads have been found to be particularly effective. MP35N® alloy (anonmagnetic, nickel-cobalt-chromium-molybdenum alloy) which is commonlyused in parts for medical applications is also suitable. The electricalconductor has a pick-up end 26 and a stimulating end 28, and isinsulated between its ends 26, 28.

The electrical impedance of the interface between the ends 26, 28 of theconductor 24 (when implanted) and the surrounding body tissue may bereduced by enlarging the surface area of the ends 26, 28. For thatpurpose, one or both of the pick-up and stimulating ends 26, 28 formelectrical terminations 30 having sufficient surface areas for reducingthe electrical impedance of the interface between the pick-up andstimulating ends 26, 28 of the electrical conductor 24 and thesurrounding body tissues. Preferably, the pick-up end 26 forms atermination 30. The pick-up end 26 forms an electrical termination 30which has a sufficient surface area to allow a sufficient portion of theelectrical current to flow through the electrical conductor 24, inpreference to flowing through body tissue between the surface cathodicand anodic electrodes 20, 22, such that the target body tissue isstimulated to either activate or block neural impulses. The stimulatingend 28 also forms an electrical termination 30 for delivering theportion of electrical current to the target body tissue (i.e., nerve12).

Terminations 30 should have sufficient surface area for providing highconductivity contact with body tissues, and lowering the electricalimpedance between the body tissue and the conductor. If the surface areais minimal, the amount of current flowing through a conductor to thetermination is reduced to an ineffective amount. The surface arearequired may thus be determined by a knowledge of the electricalimpedance of the interface between the tissue and the terminations 30 atthe receiving and stimulating ends 26, 28. Beneficial results have beenobtained by making the surface area of metal terminations 30 at the ends26, 28 about 0.5 cm². The electrical impedance of each interface betweentissue and terminations 30 at ends 26, 28 was then about 5 times theelectrical impedance of all the subcutaneous tissue between surfaceelectrodes 20, 22. A typical value of tissue impedance is 200 ohms. Theimpedance of the conductor itself is chosen to be very small, forexample 5 ohms. In the example just given, the sum of the two interfaceimpedances of the terminations 30 plus the conductor impedance was about2000 ohms, that is to say about ten times the tissue impedance. Thusabout 10% of the current applied between surface electrodes 20, 22 flowsthrough conductor 24 to the target tissue. In the case of the targettissue being a nerve 12 supplying a muscle 16, the amount of currentbetween surface electrodes 20, 22 required to produce a useful musclecontraction of the target muscle 16 then remains below the thresholdlevel of activation of nerve endings in the subcutaneous tissueimmediately between surface electrodes 20, 22. This is a beneficialrelationship, because it means that target muscles 16 can be activatedwith little or no local sensation under the surface electrodes 20, 22.

Terminations 30 of various shapes, materials and spatial arrangementscan be used; for example, terminations 30 can provide an enlargedsurface in the form of a coil, spiral, cuff, rod, or a plate or sheet inthe form of an oval or polygon. As an example, FIG. 1 illustrates atermination 30 as a plate or sheet in the form of an oval at the pick-upend 26 of the electrical conductor 24, and in the form of a cuff at thestimulating end 28. The cuff or a portion thereof can encircle orpartially encircle the entirety or part of the nerve sheath 14 of thenerve 12. The cuff or a portion thereof can be positioned proximate tothe nerve sheath 14, or the inner surface of the cuff or a portionthereof can directly contact the nerve sheath 14.

Beneficial results are obtained with stainless-steel plates or sheets inthe form of an oval which is about 0.5 cm² in area and 1 mm thick, ormade of metal foil and stainless-steel mesh and being about 0.5 cm² insurface area and 0.3 mm thick. For terminations 30 of conductors withnerve cuffs, nerve cuffs made of metal foil or stainless-steel mesh andbeing 0.5 to 1 cm² in surface area and 0.3 mm thick are suitable.Further, silastic elastomer cuffs ranging from 5 mm to 15 mm in length,4 mm to 6 mm inside diameter, and 1 mm thick are suitable.

Terminations 30 can be formed from uninsulated ends 26, 28 of theelectrical conductor 24, or from other conductive or capacitivematerials. Terminations 30 can be formed by coiling, spiraling orweaving long, uninsulated lengths of the pick-up or stimulating ends 26,28 to provide a sufficient surface. The surface area of the terminationis thus “enlarged” relative to the surface area of a shorter length ofthe electrical conductor 24. This raises the effective surface area ofthe terminations 30 within a small space to provide higher conductivitycontact with body tissues, and to lower the electrical impedance betweenthe body tissue and the conductor 24 to allow current flow in theconductor in preference to in the body tissue. Sufficient current flowis thereby provided in the conductor 24 to stimulate the target tissue.Alternatively, prefabricated terminations 30 (for example, plates orsheets in the form of ovals or polygons) can be attached directly to thepick-up and stimulating ends 26, 28. Further, terminations 30 can becoated or modified with conductive materials to maximize the flow ofelectrical current through the target body tissue.

The spatial arrangement of the terminations 30 can be varied; forexample, multiple terminations 30 can also be applied to different partsof a body tissue (Grill et al., 1996). Advantageously, the terminations30 themselves can be in the form of closely-spaced contacts enclosedwithin an embracing cuff 32 placed around the nerve 12. The embracingcuff 32 can be formed from conductive silicone rubber.

Electrical impedance may be further reduced by providing conductive orcapacitive coatings, or an oxide layer on the terminations 30. Thecoating can be selected from a material whose structural or electricalproperties improve the electrical conductance between the tissue and theconductor, for example, by providing a complex surface into which tissuecan grow (for example, a polymer such as poly-diethoxy-thiophene, orsuitable oxide layers including tantalum and sintered iridium). Inaddition, the terminations 30 can have coatings which provide ananti-inflammatory, anti-bacterial or tissue ingrowth effect. The coatingcan be a substance selected from an anti-inflammatory agent,antibacterial agent, antibiotic, or a tissue ingrowth promoter.

Optionally, performance of the invention can be improved by implantingan electrical return conductor 34 of sufficient length to extend fromthe target body tissue to subcutaneous tissue located below the surfaceanodic electrode 22. The electrical return conductor 34 provides alow-impedance conductive pathway from the target body tissue to thesurface anodic electrode 22, thereby concentrating the electric fieldthrough the target tissue. The electrical return conductor 34 can beformed from a metal wire, carbon fibers, a conductive rubber or otherconductive polymer, or a conductive salt solution in rubber. Theelectrical return conductor 34 has a collecting end 36 and a returningend 38, and is insulated between its ends 36, 38. Both the collectingend 36 and the returning end 38 form electrical terminations 30 (asdescribed above) for reducing the electrical impedance of the interfacebetween the collecting end 36 and returning end 38 of the electricalreturn conductor 34 and the surrounding body tissues. The collecting end36 forms an electrical termination 30 (shown in FIG. 1 in the form of acuff), which has a sufficient surface area to allow a portion of theelectrical current delivered to the target body tissue to return throughthe electrical return conductor 34 in preference to returning throughbody tissue. The returning end 38 forms an electrical termination 30(shown in FIG. 1 as a plate or sheet in the form of an oval) whichreturns the electrical current to the surface anodic electrode 22 viathe subcutaneous tissue and skin underlying the surface anodic electrode22.

A power source 40 (shown in FIGS. 2-4) provides operating power to astimulator (not illustrated) which is external to the subject's body.The stimulator is electrically connected to the surface cathodic andanodic electrodes 20, 22 to supply electrical current to the surfacecathodic and anodic electrodes 20, 22. The current can be resistive orcapacitive, depending on the net impedance encountered between theelectrodes 20, 22.

Although most of the electrical current flows through the body tissuesin proximity to the surface cathodic and anodic electrodes 20, 22, thereis flow of electrical current through the electrical conductor 24, nerve12, and electrical return conductor 34. As shown in FIG. 1, the surfacecathodic electrode 20 is positioned over the pick-up end 26 of theelectrical conductor 24, so that a portion of the current is transmittedthrough the conductor 24 to the target body tissue, and current flowsthrough the target body tissue and returns to the anodic surfaceelectrode 22 through body tissues. This can also be achieved through theimplanted electrical return conductor 34 extending between the targetbody tissue and subcutaneous tissue located below the surface anodicelectrode 22.

The complete electrical path of the portion of the electrical current isas follows: cathodic wire 42, surface cathodic electrode 20, skin 10,termination 30, pick-up end 26, electrical conductor 24, stimulating end28, termination 30, nerve sheath 14, nerve 12, termination 30,collecting end 36, electrical return conductor 34, returning end 38,termination 30, skin 10, surface anodic electrode 22 and anodic wire 44.The pulses of electrical current can elicit action potentials which areconducted along nerve 12 to muscle 16, causing it to contract.Alternatively, electrical current in the form of high frequencywaveforms can block action potentials conducted along nerve 12 to muscle16 to prevent muscle contractions.

Various disorders are amenable to treatment by the invention as shown inFIG. 1. As described below, the implanted passive electrical conductorsof the present invention are capable of routing electrical current tostimulate various target body tissues to either activate or block neuralimpulses depending upon the frequency and disorder to be treated.Applications have been provided below to illustrate examples of targetbody tissues and disorders for which the invention is beneficial.

B. Activation of Neural Impulses Using the Router System

In some pathological states, transmission of action potentials isimpaired; thus, activation of neural impulses is required to restorenormal functioning. In the present invention, the stimulator can supplydirect, pulsatile or alternating current between the surface cathodicand anodic electrodes 20, 22 to cause the portion of the electricalcurrent to flow through the implant 18 sufficient to stimulate thetarget body tissue to activate neural impulses.

Exemplary pulse parameters of electrical current flowing between thesurface cathodic and anodic electrodes 20, 22 for activation of neuralimpulses are as follows: biphasic current pulses, 30 pulses per second,each phase 200 microseconds in duration, and a peak current per pulseranging from 0.7 to 2 milliampere. Beneficial results can be obtainedwith rectangular, feedback-controlled current pulse waveforms, althoughother waveforms and modes of control of current or voltage have alsobeen found to give satisfactory results. The inventor has discoveredthat between 10% and 20% of the current flowing between the surfaceelectrodes 20, 22 is propagated through an implanted conductor 24, evenwhen there is no electrical return conductor 34. The type of current maybe dependent upon the application for which the invention is intended;for example, continuous current would be applied, rather than pulsatilecurrent, when the target body tissue is bone and promotion of bonegrowth is desired.

As is known to those skilled in the art, the electric currents deliveredby a pulse generator to a plurality of electrodes 20, 22 may beindependently controlled with the use of an interleaved pulse train.This comprises a sequence of stimulus pulses of different amplitudes,the pulses separated in time by a few milliseconds and delivered to eachelectrode in turn, the sequence as a whole being repeated at a rate suchas 30 times per second. The amplitudes of the pulses flowing througheach electrode may thereby be controlled independently.

For activation, low frequencies are generally used, for example, afrequency in the range of between 1 and 100 Hz, or alternatively, in therange of between 1 and 50 Hz. Still alternatively, the frequency can bein the range of between 1 and 20 Hz.

As an example, FIG. 2 illustrates the invention for use in the treatmentof a movement disorder requiring activation of the median nerve 46. Themedian nerve 46 innervates most of the flexor muscles in front of theforearm, most of the short muscles of the thumb, and the short musclesof the hand. A subject's arm 48 is illustrated with the implant 18implanted in the forearm. The electrical conductor 24 is illustratedwith its pick-up end 26 forming a termination 30 for receiving theelectrical current from the surface cathodic electrode 20. Thestimulating end 28 forms a termination 30 for delivering the electricalcurrent to the median nerve 46. A surface anodic electrode 22 ispositioned on the skin 10. A flow of electrical current from the powersource 40 is supplied via cathodic wire 42 into the skin 10 at thesurface cathodic electrode 20 and the surface anodic electrode 22 viaanodic wire 44. The electrical current flows through the termination 30,the pick-up end 26, the electrical conductor 24, the stimulating end 28,a portion of the median nerve 46, the tissue between stimulating end 28and surface anodic electrode 22 including the skin underlying electrode22, the surface anodic electrode 22, anodic wire 44 and the power source40, thus completing the electrical circuit. Some of the current flowingbetween the stimulating end 28 and the surface anodic electrode 22passes through the target body tissue (in this example, median nerve46), thereby causing the muscle 16 of the arm 48 to be stimulated.

As a further example, FIG. 3 again illustrates the invention for use inthe treatment of a movement disorder requiring activation of the mediannerve 46. However, in addition to the components shown in FIG. 2, FIG. 3illustrates an electrical return conductor 34. The electrical circuit isessentially the same as that described for FIG. 2, with the exceptionthat after flowing through the stimulating end 28 and the median nerve46, the electrical current flows through termination 30, the collectingend 36, the electrical return conductor 34, the returning end 38,termination 30, the surface anodic electrode 22, anodic wire 44 and thepower source 40, thus completing the electrical circuit. Advantageously,the electrical return conductor 34 acts to collect electrical currentflowing through the target body tissue (i.e., median nerve 46) from theelectrical conductor 24 and provides a low impedance pathway back to thesurface anodic electrode 22, thereby concentrating the electric fieldthrough the target body tissue (i.e., median nerve 46).

As yet a further example, FIG. 4 illustrates a plurality of implants 18for electrically stimulating more than one target body tissueindependently or in unison to activate neural impulses. Each implant 18is implanted entirely under the subject's skin 10 and is of a sufficientlength to extend to a different target body tissue. The presence ofmultiple implants 18 necessitates positioning of a plurality of surfacecathodic electrodes 20, and one or more surface anodic electrodes 22appropriately relative to the implants 18 to stimulate the differenttarget body tissues independently or in unison. FIG. 4 illustrates theinvention for use in the treatment of a movement disorder requiringstimulation of the median nerve 46 and the radial nerve 50. The radialnerve 50 innervates extensor muscles on the back of the arm and forearm,the short muscles of the thumb, and the extensor muscles of the indexfinger. Two separate surface cathodic electrodes 20 are eachelectrically connected via two separate cathodic wires 42 to astimulator (not illustrated) operated by the power source 40. Electricalcurrent is transmitted to the two separate electrical conductors 24, oneof which extends to the median nerve 46, and the other to the radialnerve 50. An electrical return conductor 34 extends from the targettissue (i.e., below the median nerve 46) to subcutaneous tissue locatedbelow one surface anodic electrode 22.

The electrical path of the current is as follows: cathodic wire 42, thesurface cathodic electrodes 20, the skin 10, termination 30, the pick-upend 26, the electrical conductor 24, the stimulating end 28, termination30, the median nerve 46 and/or radial nerve 50, termination 30,collecting end 36, electrical return conductor 34, returning end 38,termination 30, surface anodic electrode 22, anodic wire 44, and powersource 40. The median nerve 46 and radial nerve 50 can be stimulatedeither independently by pulsatile electrical current to provide firstly,a flexion or upward position of the wrist and finger closing (via themedian nerve 46), then secondly, extension or downward position of thewrist and finger extension (via the radial nerve 50). Alternatively, themedian nerve 46 and radial nerve 50 can be stimulated simultaneously forexample, to straighten the hand (i.e., position the wrist horizontally).It will be appreciated by those skilled in the art that the inventioncan be applied to other target body tissues and disorders whereactivation of neural impulses is needed to restore normal functioning.

C. Blockade of Neural Impulses Using the Router System

In some pathological states, action potentials are transmitted which donot serve a useful purpose; hence, blocking of unnecessary nerveimpulses is required to restore normal functioning. The inventionprovides a method for treating disorders by applying electrical currentin the form of cyclical waveforms at a frequency capable of blocking atarget body tissue so as to treat the disorder. Electrical currentwaveforms are generated at a frequency which is high enough to causeconduction block in target neural tissues. For example, the electricalcurrent can be applied in the form of pulses, typically 20 to 1,000microseconds in duration at a rate high enough to cause conduction blockin the target axons. The frequency and pulse parameters, including pulseamplitude, pulse duration and pulse rate, depend upon many factors thatare well known to those skilled in the art; for example, the type ofnerve to be blocked (either in the peripheral or central nervoussystem), the tissue which the nerve innervates (e.g., autonomic organssuch as the bladder, or somatic organs such as muscle), the size of thenerve, the subject to be treated, the type of condition, the severity ofthe condition, and the receptiveness of the subject to the treatment.

A wide range of frequencies from 100 Hz to 30 kHz has been reported toproduce an effective block depending upon various parameters among thosedescribed above and the particular stimulation technique used; forexample, 100-300 Hz for subthalamic nucleic in human deep brain toreduce motor symptoms (Ashkan et al., 2004; Filali et al., 2004); 500 Hzfor a muscle nerve (Solomonow et al., 1983); 600 Hz for a sacral nerveroot in an acute spinalized dog to achieve bladder voiding (Shaker etal., 1998); 600 Hz for the ventral sacral root to inhibit urethralsphincter contractions in chronically spinalized dogs (Abdel-Gawad etal., 2001); 200-1400 Hz for epidural stimulation in a human to moderatemotor disorders (Broseta et al., 1987); 4 kHz for the pudendal nerve incats to block external urethral sphincter contractions (Tai et al. 2004,2005); and 10-30 kHz for a peripheral nerve to treat spasticity and pain(Bhadra and Kilgore, 2005).

For blockade of neural impulses, it is required that the frequency ishigher than frequencies normally required to stimulate a nerve toconduct action potentials, and high enough to block conduction of actionpotentials in target body tissues. In general, for blocking, highfrequencies are useful, for example, the cyclical waveform can beapplied at a frequency in the range of between 100 and 30,000 Hz, oralternatively in the range of between 100 and 20,000 Hz. Stillalternatively, the cyclical waveform can be applied at a frequency inthe range of between 100 and 10,000 Hz, or in the range between 200 and5,000 Hz.

Example 1 (see below) illustrates use of the present invention, theresults of which suggest that stimulation with an amplitude greater than3 mA and a frequency greater than 200 Hz is capable of blockingtransmission of neural impulses in the pudendal nerve of a cat. It ishighly advantageous that the stimulator of the invention is external tothe subject's body and supplies high frequency electrical currentwaveforms to the surface cathodic and anodic electrodes 20, 22positioned externally on the subject's skin. A wide range of pulseparameters can be readily and easily tested and adjusted to determineoptimal parameters for achieving the desired physiological result in asubject following implantation of the electrical conductor 24.

Exemplary pulse parameters of high frequency trains of electricalcurrent flowing between surface cathodic and anodic electrodes 20, 22are as follows: current-controlled or voltage-controlled biphasicpulses, with phase durations ranging from 10 microseconds to 1,000microseconds, or cyclical waveforms such as sinusoids or triangular,rectangular or sawtooth waveforms.

Blockade of a nerve impulse using the invention is reversible at allfrequencies such that when high frequency stimulation is turned off, thenerve can again propagate action potentials and no damage has beenincurred. Further, partial or complete blocking of a nerve impulse canbe achieved depending upon the condition to be treated. For example,complete blocking of sensory nerves may be required to alleviate pain,while partial or complete blocking of sensory and motor nerves may beneeded to reduce spasticity.

Other embodiments of the invention are possible. For instance, aplurality of implants 18 for electrically blocking more than one targetbody tissue independently or in unison can be used. The presence ofmultiple implants 18 necessitates positioning of a plurality of surfacecathodic electrodes 20, and one or more surface anodic electrodes 22appropriately relative to the implants 18 to block the different targetbody tissues independently or in unison.

In another embodiment, a plurality of implants 18 for electricallyactivating neural impulses in more than one body tissue independently orin unison can be used concomitantly with the above implants 18 forelectrically blocking neural impulses in target body tissues. Twoseparate signals are required, with a low frequency signal required toactivate a nerve, and a high frequency signal required to block anothernerve. For example, bladder voiding can be achieved by applying lowfrequency pulse trains to the sacral nerve root S1, which elicitsbladder and sphincter contractions, and by simultaneously applying highfrequency waveforms to the pudendal nerve to block the sphinctercontractions induced by stimulating the sacral nerve root S1.

Various disorders requiring blocking of neural impulses are amenable totreatment by the invention as shown in FIG. 1. As an example, theinvention can be used to achieve bladder voiding (see Example 1). Whenthe bladder is full, nerve signals are normally sent to the brain toconvey the need to urinate. In response, the brain initiates acoordinated response in which the bladder wall contracts, creatingpressure that forces urine into the urethra, while a sphincter,surrounding the urethra, opens to allow urine to flow out. In certaindisorders, for example spinal cord injury, the bladder is generallyunable to empty because of hyper-reflexive contractions of the externalsphincter. The closure of the sphincter is maintained by reflexesintended to maintain continence, which can no longer be suppressed bysignals from the brain. The pudendal nerve innervates the musculature ofthe pelvic floor and the external urethral and external anal sphincters.The motor component of the urinary branch of the pudendal nerveactivates the external urethral sphincter muscle. Blocking this branchrelaxes the sphincter and allows bladder emptying.

To achieve bladder voiding, the electrical conductor 24 is implanted inthe subject with its stimulating end 28 positioned proximate or incontact with the pudendal nerve. The pick-up end 26 of the electricalconductor 24 extends into subcutaneous tissue located below the surfacecathodic electrode 20. The surface cathodic and anodic electrodes 20, 22are positioned preferably on the subject's skin above the hips. Sincethe pudendal nerve is present on both the left and right sides of thebody, two electrical conductors 24 can optionally be positioned on bothsides to achieve blocking. This would necessitate one surface anodicelectrode 20, and either one or two surface cathodic electrodes 22. Theelectrical conductor 24 provides a conductive pathway for at least aportion of the electrical current flowing between the surface cathodicand anodic electrodes 20, 22 in the form of high frequency waveforms andtransmits that portion of the electrical current to the pudendal nerve.Blocking of the pudendal nerve by stimulation with high frequencyelectrical pulses subsequently causes the urethral sphincter to open (asobserved by a sudden large drop in intraurethral pressure), allowingbladder voiding. The pudendal nerve is blocked to allow bladder voidinguntil the bladder is empty.

The invention can also be used to alleviate pain, which generally refersto a localized sensation of discomfort resulting from the stimulation ofspecialized nerve endings. Peripheral nerves are nerves and gangliaoutside the brain and spinal cord. In a mixed peripheral nerve, thethinnest exteroceptive sensory fibers convey impulses which areinterpreted in sensation as pain. The present invention can thus be usedto block sensory axons in peripheral nerves to reduce pain. For example,trigeminal neuralgia is a repeated and incapacitating pain affecting thelower portion of the face and arising from malfunction of the trigeminalnerve, which carries sensory information from the face to the brain andcontrols the muscles involved in chewing. The electrical conductor 24 isimplanted having its pick-up end 26 proximate or in contact with acranial nerve (such as the trigeminal nerve) and its stimulating end 28positioned subcutaneously within the head. Surface cathodic and anodicelectrodes 20, 22 are positioned on the skin of the head. The electricalconductor 24 provides a conductive pathway for at least a portion of theelectrical current flowing between the surface cathodic and anodicelectrodes 20, 22 in the form of high frequency cyclical waveformstransmits that portion of the electrical current to the trigeminalnerve. Blocking of the trigeminal nerve may subsequently reduce pain inpatients with trigeminal neuralgia.

Spasticity, tremor and/or muscle weakness is an example of a furtherdisorder to which the invention is applicable for blocking of neuralimpulses. Spasticity is characterized by a state of hypertonicity (i.e.,an excessive tone of skeletal muscle with heightened deep tendonreflexes), and can cause muscle stiffness and awkward movements. It canoccur as a result of stroke, cerebral palsy, multiple sclerosis orspinal cord injury. Nerve fibers involved with spasticity includesensory and motor nerves. The present invention can be used to blocksensory and motor nerves to block muscle spasms. Referring again to FIG.3, the median nerve 46 can be blocked (rather than activated aspreviously described) to alleviate flexure spasms occurring due to astroke or multiple sclerosis. A flow of electrical current from thepower source 40 is supplied in the form of high frequency cyclicalwaveforms via cathodic wire 42 into the skin 10 at the surface cathodicelectrode 20 and the surface anodic electrode 22 via anodic wire 44. Theelectrical current flows through the termination 30, the pick-up end 26,the electrical conductor 24, the stimulating end 28, a portion of themedian nerve 46, the tissue between stimulating end 28 and surfaceanodic electrode 22 including the skin underlying electrode 22, thesurface anodic electrode 22, anodic wire 44 and the power source 40,thus completing the electrical circuit. Some of the current flowingbetween the stimulating end 28 and the surface anodic electrode 22passes through the target body tissue (in this example, median nerve46), thereby blocking nerve impulses along the median nerve 46 andpreventing contraction of the muscle 16 of the arm 48.

The invention can also be used to reduce pain and spasticity by blockingthe spinal cord. As an example, back pain or leg muscle spasms may bealleviated by blocking spinal nerves in the lumbar spine. The lumbarspinal nerves (L1 to L5) supply the lower parts of the abdomen and theback, the buttocks, some parts of the external genital organs, and partsof the legs. The electrical conductor 24 is implanted with itsstimulating end 28 positioned between lumbar vertebrae into the lumbarspinal canal. The stimulating end 28 is placed proximate to the epiduralspace between the dura mater and the walls of the spinal canal. Thepick-up end 26 is positioned subcutaneously in the lower back of thebody. Surface cathodic and anodic electrodes 20, 22 are positioned onthe skin of the lower back. The electrical conductor 24 provides aconductive pathway for at least a portion of the electrical currentflowing between the surface cathodic and anodic electrodes 20, 22 in theform of high frequency cyclical waveforms and transmits that portion ofthe electrical current to the spinal cord. Blocking of the lumbar spinalnerves may subsequently reduce pain or spasticity in affected regions ofthe lower body.

The invention can be used to treat pathological tremor, Parkinson'sdisease, dystonia and other disorders by blocking deep brain nuclei.Such target tissues can include the basal ganglia which includes thesubthalamic nucleus and substantia nigra. Parkinson's disease is adisorder of the basal ganglia. The electrical conductor 24 is implantedwith its stimulating end 28 positioned proximate or in contact with thebasal ganglia. The pick-up end 26 is positioned subcutaneously withinthe head. Surface cathodic and anodic electrodes 20, 22 are positionedon the skin of the head. The electrical conductor 24 provides aconductive pathway for at least a portion of the electrical currentflowing between the surface cathodic and anodic electrodes 20, 22 in theform of high frequency waveforms and transmits that portion of theelectrical current to the basal ganglia. The electrical current blocksthe electrical signals that cause symptoms of movement disorders. Thepresent invention may thus be useful in blocking the basal ganglia orother target deep brain nuclei to treat disorders in which movement isimpaired.

When a Markush group or other grouping is used herein, all individualmembers of the group and all combinations and possible subcombinationsof the group are intended to be individually included in the disclosure.Every formulation or combination of components described or exemplifiedherein can be used to practice the invention, unless otherwise stated.One of ordinary skill in the art will appreciate that methods, deviceelements, and materials other than those specifically exemplified can beemployed in the practice of the invention without resort to undueexperimentation. All art-known functional equivalents, of any suchmethods, device elements, and materials are intended to be included inthis invention. Whenever a range is given in the specification, forexample, a temperature range, a frequency range, a time range, or acomposition range, all intermediate ranges and all subranges, as wellas, all individual values included in the ranges given are intended tobe included in the disclosure. Any one or more individual members of arange or group disclosed herein can be excluded from a claim of thisinvention. The invention illustratively described herein suitably may bepracticed in the absence of any element or elements, limitation orlimitations which is not specifically disclosed herein.

As used herein, “comprising” is synonymous with “including,”“containing,” or “characterized by,” and is inclusive or open-ended anddoes not exclude additional, unrecited elements or method steps. As usedherein, “consisting of” excludes any element, step, or ingredient notspecified in the claim element. As used herein, “consisting essentiallyof” does not exclude materials or steps that do not materially affectthe basic and novel characteristics of the claim. Any recitation hereinof the term “comprising”, particularly in a description of components ofa composition or in a description of elements of a device, can beexchanged with “consisting essentially of” or “consisting of”.

Although the description herein contains many specificities, theseshould not be construed as limiting the scope of the invention, but asmerely providing illustrations of some of the embodiments of theinvention. Each reference cited herein is hereby incorporated byreference in its entirety. However, if any inconsistency arises betweena cited reference and the present disclosure, the present disclosuretakes precedence. Some references provided herein are incorporated byreference herein to provide details concerning the state of the artprior to the filing of this application, other references may be citedto provide additional or alternative device elements, additional oralternative materials, additional or alternative methods of analysis orapplication of the invention.

The invention is further illustrated in the following non-limitingExamples.

THE EXAMPLES Example 1

Two experiments were performed on anesthetized cats using the presentinvention to achieve high-frequency blockade of the pudendal nerve.

Methods

Surgical procedures: Cats were pre-operatively medicated withacepromazine (0.25 mg/kg intramuscular), glycopyrrolate (0.01 mg/kgintramuscular) and buprenorphine (0.01 mg/kg intramuscular) andanesthetized with a mixture of isoflurane (2-3% in carbogen, flow rate 2L/min). The trachea was cannulated and connected to a closed loopanesthetic system that monitored respiration rate and assistedventilation. One jugular or cephalic vein was catheterized to allowadministration of fluids and drugs. The bladder was exposed via amidline abdominal incision and catheterized to allow the addition andwithdrawal of fluids and the measurement of pressure within the bladderwith a pressure transducer (see below). A second catheter (Kendall,closed end Tom Cat catheter) was inserted into the urethra and connectedto a second pressure transducer to allow measurement of intraurethralpressure. The pudendal nerves were exposed by incisions lateral to thebase of the tail. Cuff or hook electrodes were placed on the pudendalnerve or its branches. At the end of the experiment, the animals wereeuthanized with Euthanyl™.

Pressure measurements: Bladder pressure and urethral pressure weremonitored in most stimulation trials. The urethral catheter was attachedto a Harvard Apparatus Pump 22 syringe pump and set to infuse saline at0.2 mL/min to allow measurement of intraurethral pressure as per themethod of Brown and Wickham. Both the bladder and urethral catheterswere connected via Luer ports to Neurolog NL108D4/10 domes and NL108T4isolated pressure transducers. The pressure signals were low-passfiltered at 30 Hz and sampled at a rate of 100 samples per second usinga CED 1401 laboratory computer interface and sampling software.

Stimulators: Neurolog (Digitimer Ltd., Welwyn Garden City, UK) modulesNL304 (period generator), NL403 (delay-width), NL510 (pulse buffer) andNL800 (stimulus isolator) were used to deliver constant currentmonophasic pulses and Grass (Grass-Telefactor, West Warwick, R.I., USA)SD9 and S48 stimulators were used to deliver constant voltage monophasicpulses.

Means of delivering stimulation: Two types of stimulation were tested,namely direct stimulation, and stimulus routing using the presentinvention. In direct stimulation, a stimulating electrode was placed onthe exposed pudendal nerve and connected via an insulated lead wire tothe cathodal output of the Grass stimulator. A second (indifferent)electrode comprising an alligator clip attached to the incised skin nearthe exposed pudendal nerve was connected to the anodal output of theGrass stimulator. In stimulus routing using the present invention, animplanted electrode comprising a pick-up end in the form of a metal diskor coiled wire connected via an insulated lead wire to a stimulating endwas implanted so that the pick-up end was located subcutaneously overthe lumbar spine under a surface cathodal electrode and the stimulatingend was in contact with a pudendal nerve. The surface cathodal electrodewas a conductive gel electrode (Kendall, H59P) applied to the shavedskin overlying the pick-up end and connected to the cathodal output ofthe Neurolog stimulator. A second surface electrode was placed a fewcentimeters rostral to the cathodal electrode and connected to theanodal output of the Neurolog stimulator.

Low frequency (20 Hz) direct stimulation via a hook electrode placedproximally on the pudendal nerve was used to elicit contractions of theexternal urethral sphincter. These contractions were monitored in termsof intraurethral pressure as increases in intrauthreal pressure areindicative of contractions of the external urethral sphincter. Duringperiods of low-frequency direct stimulation, bursts of high-frequencystimulation were delivered via the router system through a hookelectrode placed more distally on the pudendal nerve. The efficacy ofthe router-mediated high-frequency stimulation in blocking the nerveactivity evoked by the direct low frequency stimulation was therebydetermined.

Results

FIGS. 5A and 5B shows the results obtained in one animal whenstimulation frequency and amplitude were varied and the efficacy of thepudendal nerve block was observed. The efficacy was measured byobserving changes in the intraurethral pressure with the open port ofthe intraurethral catheter placed in the region of the external urethralsphincter. The right pudendal nerve was stimulated proximally at lowfrequency to elicit external urethral sphincter contractions while highfrequency stimulation was applied distally to block the contractions.The maximum decrease in intraurethral pressure (FIG. 5A) was defined asthe difference between the intraurethral pressure immediately beforehigh frequency stimulation was applied and the minimal pressure obtainedduring high frequency stimulation. There appeared to be a trend towardslarger decreases in intraurethral pressure at higher stimulationamplitudes. Blocking was obtained at all stimulation frequenciesexamined (i.e., 200, 500, 1000 and 2000 Hz).

FIG. 5B summarizes the effect of stimulation pulse frequency andamplitude on the ability of high frequency stimulation to return theintraurethral pressure to baseline. This provides a measure of thecompleteness of the block. The most complete blocking was achieved withstimulation amplitudes of 3 mA and higher. At a stimulation pulseamplitude of 3 mA, all tested frequencies (i.e., 200, 500, 1000 and 2000Hz) elicited a nearly complete block. There was a general trend towardsa more complete block at higher stimulation pulse amplitudes. A Y-axisvalue of zero indicates that the intraurethral pressure during highfrequency stimulation was equal to the pre-stimulation baselinepressure.

FIGS. 6A and 6B show the effect of stimulation pulse amplitude onpudendal nerve blocking in one animal. The traces representintraurethral pressure obtained at 1 mA (FIG. 6A) and at 3 mA (FIG. 6B),the dashed bars indicate duration of low frequency stimulation and thesolid bars indicate the duration of high frequency stimulation. Lowfrequency stimulation was applied proximally on the pudendal nerve witha monopolar hook electrode directly connected to the cathodal output ofthe Grass stimulus generator. High frequency stimulation was applieddistally on the pudendal nerve with a monopolar hook electrode connectedto the Neurolog stimulus generator via the stimulus routing system ofthe present invention. The anodal indifferent surface electrode wasplaced a few centimeters rostral to the cathodal surface electrode. Lowfrequency stimulation was delivered at a frequency of 20 Hz with pulseshaving an amplitude of 520 μA and a pulse width of 300 μs. Highfrequency stimulation was delivered at a frequency of 1 kHz with pulseshaving a pulse width of 100 μs. Stimulation with 1 mA pulse amplitudeshad very little effect on the intraurethral pressure and elicited verylittle block of sphincter activity. However, with the stimulation pulseamplitude increased to 3 mA, a complete temporary and reversible blockof sphincter activity was achieved.

In the trials shown in FIGS. 7A and 7B, the stimulation frequency was 2kHz. At 6 mA pulse amplitudes (FIG. 7A), a nearly complete block wasachieved, but contractions of the leg under the surface cathodalelectrode accompanied the stimulation. These contractions weremaintained for the duration of the stimulation. At pulse amplitudes of 3mA, similar blocking efficacy was achieved without concomitant legcontractions (FIG. 7B). In this trial, low frequency stimulation(duration indicated by dashed bars) was delivered at a frequency of 20Hz with pulses having an amplitude of 300 μA and a pulse width of 200μs, while high frequency stimulation (duration indicated by solid bars)was delivered at a frequency of 2 kHz with pulses having a pulse widthof 150 μs.

In further trials, in addition to low frequency stimulation of theproximal pudendal nerve and high frequency stimulation of the distalpudendal nerve, increases in bladder pressure were generated by manuallyapplied abdominal pressure. FIG. 8 shows an example where this combinedprocedure was performed. FIG. 8 shows the effect of pudendal nerveblocking on intraurethral pressure in one animal. The solid trace isintraurethral pressure, the dotted trace is bladder pressure, the dashedbar indicates duration of low frequency stimulation and the solid barsindicate duration of high frequency stimulation. Low frequencystimulation was delivered at a frequency of 20 Hz with pulses having anamplitude of 330 μA and a pulse width of 200 μs. High frequencystimulation was delivered at a frequency of 2 kHz with pulses having anamplitude of 4 mA and a pulse width of 100 μs. Initial low frequencystimulation was used to generate an external urethral sphinctercontraction after which the bladder pressure was increased by manualapplication of pressure to the abdomen. No voiding occurred during thefirst 20 seconds as intraurethral pressure was maintained higher thanthe manually generated bladder pressure by the direct pudendal nervestimulation. Once high frequency stimulation of the distal pudendalnerve was applied, intraurethral pressure became equal to bladderpressure, indicating that the external sphincter was relaxed, andvoiding occurred.

Several trials were performed in which the intraurethral catheter wasremoved to examine voiding. Complete voiding was achieved when highfrequency stimulation was used to block low frequencystimulation-induced external urethral sphincter contractions and thebladder pressure was increased manually. In general, the results abovesuggest that use of the present invention and stimulation with anamplitude greater than 3 mA and a frequency greater than 200 Hzcontributes to blocking transmission of activity in the pudendal nerve.Determination of stimulation parameters to produce an optimal block isunder investigation. It will be understood by those skilled in the artthat other stimulation parameters may produce better blocking results,particularly in other parts of the peripheral and central nervoussystems. It will also be understood that it will be desirable todetermine the stimulation parameters required to produce optimal nerveblocking on an individual basis, as these parameters may vary fromsubject to subject, depending upon the characteristics of the skin aswell as the precise positioning of the components of the presentinvention.

D. Advantages of the Router System

As described above, the invention thus provides several advantages,primarily the capability of stimulating a target body tissue to eitheractivate or block neural impulses depending upon the frequency and thedisorder to be treated. Further, the present invention includes a meansof “remote” stimulation, that is the surface cathodic and anodicelectrodes 20, 22 do not have to be positioned over target body tissues.Remote target body tissues, such as nerves 12, can be stimulated toactivate or block neural impulses from closely spaced surface cathodicand anodic electrodes 20, 22, by routing current through separateelectrical conductors 24 simultaneously to several remote target bodytissues.

Further, greater selectivity is provided in stimulating target bodytissues to activate or block neural impulses. The electrical conductor24 extends to a specific target body tissue, or multiple electricalconductors 24 can extend to multiple target body tissues. Stimulation isthus specific to the target body tissues, and stimulation of non-targetbody tissues is avoided. As an electrical conductor 24 of sufficientlength is used to reach target body tissues, stimulation of target bodytissues which are positioned deep within the body or organs such as themuscles, brain, cochlea, optic nerve, heart, bladder, urethra, kidneysand bones, can be achieved.

Stimulation to activate or block neural impulses is reproducible atwill. The electrical conductor 24 is passive and can remain permanentlyimplanted with the pick-up end 26 under the skin 10 beneath the site atwhich the surface cathodic electrode 20 would be placed, and thestimulating end 28 positioned proximate to the target body tissue. Tothe inventor's knowledge, difficulty has been encountered in positioningsurface electrodes accurately to obtain acceptable selectivity ofstimulation of body tissues. The inventor has discovered thatsurprisingly, the invention requires far less accuracy in positioning ofthe surface cathodic and anodic electrodes 20, 22; consequently,stimulation of body tissues to activate or block neural impulses is moreaccurately reproducible.

Further, the invention avoids problems inherent in other forms ofstimulation. The conductors (i.e., electrical conductor 24, electricalreturn conductor 34) do not emerge through the skin, thus reducing therisk of infection which may arise with percutaneous devices. There is noneed to construct an implant housing its own stimulator, signalgenerator or power source, or to provide radio-frequency or othertelemetric command signals through the skin.

It will be apparent to one skilled in the art that modifications may bemade to the illustrated embodiment without departing from the spirit andscope of the invention as hereinafter defined in the claims.

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All publications mentioned in this specification are indicative of thelevel of skill in the art to which this invention pertains. Allpublications are herein incorporated by reference to the same extent asif each individual publication was specifically and individuallyindicated to be incorporated by reference. Although the foregoinginvention has been described in some detail by way of illustration andexample, for purposes of clarity and understanding it will be understoodthat certain changes and modifications may be made without departingfrom the scope or spirit of the invention as defined by the followingclaims.

The invention claimed is:
 1. A system for electrically stimulating a target body tissue in a subject, comprising: a surface cathodic electrode and a surface anodic electrode configured to make electrical contact with the subject's skin and to transmit electrical current when positioned in a spaced relationship on the subject's skin; a stimulator external to the subject's body, electrically connected to the surface cathodic electrode and the surface anodic electrode, the stimulator being configured to supply direct, pulsatile, or alternating current to the surface cathodic electrode and the surface anodic electrode at a frequency from 1 Hz to 30 kHz; and an implant configured to pick up a portion of the electrical current flowing between the surface cathodic electrode and the surface anodic electrode and to transmit the portion of the electrical current to the target body tissue, the implant comprising a passive electrical conductor of sufficient length to extend, once implanted, from subcutaneous tissue located below the surface cathodic electrode to the target body tissue, the electrical conductor having a pick-up portion and a stimulating portion and being insulated between its pick-up portion and its stimulating portion, the pick-up portion forming an electrical termination having a sufficient surface area to allow a portion of the electrical current to flow through the conductor, in preference to flowing through body tissue between the surface cathodic and anodic electrodes, and the stimulating portion forming an electrical termination for delivering the portion of electrical current to the target body tissue.
 2. The system of claim 1, further comprising an electrical return conductor of sufficient length to extend, once implanted, from the target body tissue to subcutaneous tissue located below the surface anodic electrode, the return conductor having a collecting portion and a returning portion and being insulated between its collecting portion and its returning portion, the collecting portion forming an electrical termination having a sufficient surface area to allow a portion of the current delivered to the target body tissue to return through the return conductor in preference to returning through body tissue, and the returning portion forming an electrical termination to return the electrical current to the surface anodic electrode via the subcutaneous tissue and skin underlying the surface anodic electrode.
 3. The system of claim 2, wherein at least one of the conductor and the return conductor is formed from a metal wire, carbon fibers, a conductive rubber or other conductive polymer, or a conductive salt solution in rubber.
 4. The system of claim 1, wherein the termination on at least one of the pick-up portion or the stimulating portion is an enlarged surface in the form of a coil, a spiral, a cuff, a rod, or a plate or sheet in the form of an oval or polygon.
 5. The system of claim 1, wherein the surface cathodic and anodic electrodes each comprise a conductive plate or sheet, a conductive gel electrode, a conductive rubber or polymer electrode that may be partially coated with an electrode paste or gel, or a moistened absorbent pad electrode.
 6. The system of claim 1, wherein the terminations of the pick-up and delivery portions are formed from uninsulated end portions of the conductor itself or from other conductive materials.
 7. The system of claim 1, further comprising a coating on at least one of the terminations, the coating being a conductive or capacitive coating, an oxide layer, an anti-inflammatory agent, an antibacterial agent, an antibiotic, or a tissue ingrowth promoter.
 8. The system of claim 1, wherein the stimulator is configured to supply electrical current in the form of a cyclical monophasic wave form or in the form of a cyclical biphasic waveform.
 9. The system of claim 1, wherein: the implant is one implant from a plurality of implants, each of the plurality of implants configured to electrically block target body tissue independently or in unison, each implant from the plurality of implants configured to be implanted entirely under the subject's skin and to be of a sufficient length to extend to a different target body tissue, and the surface cathodic electrode is one surface cathodic electrode from a plurality of surface cathodic electrodes, at least the surface cathodic electrode and the surface anodic electrode configured to be positioned relative to the plurality of implants to block the different target body tissues independently or in unison.
 10. The system of claim 1, wherein: the implant is one implant from a plurality of implants, each of the plurality of implants configured to electrically activate target body tissue independently or in unison, each implant from the plurality of implants configured to be implanted entirely under the subject's skin and to be of a sufficient length to extend to a different target body tissue, and the surface cathodic electrode is one surface cathodic electrode from a plurality of surface cathodic electrodes, at least the surface cathodic electrode and the surface anodic electrode configured to be positioned relative to the plurality of implants to activate the different target body tissues independently or in unison.
 11. A method comprising at least one of electrically blocking or electrically activating a target body tissue in a subject using the system of claim
 1. 12. The system of claim 1, wherein the stimulator is configured to supply electrical current in the form of a cyclical waveform at a frequency in the range of from 100 Hz to 20 kHz for blocking the target body tissue.
 13. The system of claim 1, wherein the stimulator is configured to supply electrical current in the form of a cyclical waveform at a frequency in the range of from 100 Hz to 10 kHz for blocking the target body tissue.
 14. The system of claim 1, wherein the stimulator is configured to supply electrical current in the form of a cyclical waveform at a frequency in the range of from 200 Hz to 5 kHz for blocking the target body tissue.
 15. The system of claim 1, wherein the stimulator is configured to supply electrical current in the form of a cyclical waveform at a frequency in the range of from 1 kHz to 30 kHz for blocking the target body tissue.
 16. The system of claim 1, wherein the stimulator is configured to supply electrical current in the form of a cyclical waveform at a frequency in the range of from 1 kHz to 20 kHz for blocking the target body tissue.
 17. The system of claim 1, wherein the stimulator is configured to supply electrical current in the form of a cyclical waveform at a frequency in the range of from 1 kHz to 10 kHz for blocking the target body tissue.
 18. The system of claim 1, wherein the stimulator is configured to supply electrical current at a frequency in the range of from 1 Hz to 100 Hz for activating the target body tissue.
 19. The system of claim 1, wherein the stimulator is configured to supply electrical current at a frequency in the range of from 1 Hz to 50 Hz for activating the target body tissue.
 20. The system of claim 1, wherein the stimulator is configured to supply electrical current at a frequency in the range of from 1 Hz to 20 Hz for activating the target body tissue.
 21. The system of claim 1, wherein the stimulator is configured to supply electrical current in the form of a cyclical waveform at a frequency in the range of from 100 Hz to 30 kHz for blocking the target body tissue.
 22. The system of claim 21, wherein the stimulator is configured to supply electrical current in a cyclical waveform selected from alternating current, pulsatile, sinusoidal, triangular, rectangular and sawtooth waveforms.
 23. A method of treating a disorder by electrically stimulating a target body tissue in a subject, comprising: implanting an implant entirely under the subject's skin, the implant configured to act as a conductive pathway for at least a portion of an electrical current flowing between a surface cathodic electrode and a surface anodic electrode positioned in a spaced relationship on the subject's skin and to transmit the portion of the electrical current to the target body tissue, the implant comprising a passive electrical conductor of sufficient length to extend, once implanted, from subcutaneous tissue located below the surface cathodic electrode to the target body tissue, the electrical conductor having a pick-up portion and a stimulating portion and being insulated between its pick-up portion and its stimulating portion, the pick-up portion forming an electrical termination having a sufficient surface area to allow a portion of the electrical current to flow through the conductor, in preference to flowing through body tissue between the surface cathodic electrode and the surface anodic electrode, such that the target body tissue is stimulated, and the stimulating portion forming an electrical termination to deliver the portion of electrical current to the target body tissue, the implant being implanted such that the pick-up portion is positioned in subcutaneous tissue located below the surface cathodic electrode and the stimulating portion is positioned proximate to the target body tissue; positioning the surface cathodic and anodic electrodes in a spaced relationship on the subject's skin to make electrical contact with the skin, the surface cathodic electrode being positioned over the pick-up portion of the electrical conductor such that the portion of the electrical current is transmitted through the conductor to the target body tissue, and such that the electrical current flows through the target body tissue and returns to the anodic surface electrode through body tissues or through an implanted electrical return conductor extending between the target body tissue and subcutaneous tissue located below the surface anodic electrode; and applying electrical current in at least one of a direct, pulsatile, or alternating current to at least one of the surface cathodic electrode and the surface anodic electrode, the electrical current being supplied by a stimulator external to the subject's body and electrically connected to the surface cathodic and anodic electrodes, the electrical current being applied at a frequency within the range of from 1 Hz to 30 kHz for stimulating the target body tissue.
 24. The method according to claim 23, further comprising implanting an electrical return conductor entirely under the subject's skin, the return conductor being of sufficient length to extend, once implanted, from the target tissue to subcutaneous tissue located below the surface anodic electrode, the return conductor having a collecting portion and a returning portion and being insulated between its collecting portion and its returning portion, the collecting portion forming an electrical termination having a sufficient surface area to allow a portion of the electrical current delivered to the target body tissue to return through the return conductor in preference to returning through body tissue, and the returning portion forming an electrical termination to return the electrical current to the surface anodic electrode via the subcutaneous tissue and skin underlying the surface anodic electrode.
 25. The method of claim 23, wherein electrical current is supplied at a frequency in the range of from 100 Hz to 30 kHz for blocking the target body tissue.
 26. The method of claim 25, wherein the disorder is one or more of urinary retention, incontinence, pain, an autonomic disorder, spasticity, tremor, muscle weakness, Parkinson's disease, and dystonia.
 27. The method of claim 26, wherein the body tissue is selected from a neural tissue in the peripheral or central nervous system or a nerve.
 28. The method of claim 27, wherein the electrical current is supplied at a frequency in the range of from 100 Hz to 20 kHz.
 29. The method of claim 27, wherein the electrical current is supplied at a frequency in the range of from 100 Hz to 10 kHz.
 30. The method of claim 27, wherein the electrical current is supplied at a frequency in the range of from 200 Hz to 5 kHz.
 31. The method of claim 27, wherein the electrical current is supplied at a frequency in the range of from 1 kHz to 30 kHz.
 32. The method of claim 27, wherein the electrical current is supplied at a frequency in the range of from 1 kHz to 20 kHz.
 33. The method of claim 27, wherein the electrical current is supplied at a frequency in the range of from 1 kHz to 10 kHz.
 34. The method of claim 27, wherein the stimulator is configured to supply electrical current in a cyclical monophasic waveform or in a cyclical biphasic waveform.
 35. The method of claim 27, wherein the implant is one implant from a plurality of implants, each of the plurality of implants configured to be implanted entirely under the subject's skin and being of a sufficient length to extend to a different target body tissue, and the surface cathodic electrode is one of a plurality of surface cathodic electrodes, the plurality of implants, the plurality of surface cathodic electrodes and the surface anodic electrode being collectively configured to electrically block more than one target body tissue independently or in unison, further comprising: positioning the plurality of surface cathodic electrodes and the surface anodic electrode on the subject's skin relative to the plurality of implants implanted entirely beneath the subject's skin; and supplying the electrical current to block the more than one target body tissue independently or in unison.
 36. The method of claim 23, wherein the electrical current is applied at a frequency in the range of from 1 Hz to 100 Hz for activating the target tissue.
 37. The method of claim 36, wherein the body tissue is selected from a neural tissue in the peripheral or central nervous system or a nerve.
 38. The method of claim 36, wherein the electrical current is applied at a frequency in the range of from 1 Hz to 50 Hz.
 39. The method of claim 36, wherein the implant is one implant from a plurality of implants, each of the plurality of implants configured to be implanted entirely under the subject's skin and being of a sufficient length to extend to a different target body tissue, and the surface cathodic electrode is one of a plurality of surface cathodic electrodes, the plurality of implants, the plurality of surface cathodic electrodes and the surface anodic electrode being collectively configured to electrically activate more than one target body tissue independently or in unison, further comprising: positioning the plurality of surface cathodic electrodes and the surface anodic electrode on the subject's skin relative to the plurality of implants implanted entirely beneath the subject's skin; and supplying the electrical current to activate the more than one target body tissue independently or in unison. 